Note that to simulate the real world applications, here the low resolution images are obtained by Nearest Neighbour downsampling of the high resolution test images. This is different from the common SISR algorithm evaluation routine, which utilizes Bicubic downsampling. The Nearest Neighbour sampling is known to suffer severe aliasing and blurring, whereas Bicubic downsampling implicitly performs low pass filtering before sampling, thereby largely avoids such artifacts [1]}. However, using Bicubic downsampling also implicitly assumes that the high resolution images are known, which is not the case for real applications. Therefore we only apply bicubic downsampling in the comparison experiments for fair conditions. Due to the coarse downsampling, bicubic warping has lower accuracy than bilinear warping, which is seemingly counter intuitive.
